Acid process for production of high grade molybdenum oxide



Dec. 20, 1960 s. R. ZIMMERLEY ET AL 2,965,447

ACID PROCESS FOR PRODUCTION OF HIGH GRADE MOLYBDENUM OXIDE Filed 001:.10, 1957 Molybdenum Sulfide Concentrate Roaster (2-4 hrs at 600C)Gaseous Effluent To Scrubber for recovery of Rhenium CoIcme Mme-ml AcidRotary Furnace 8 hrs at 300 to 400 C) Calcine water Leach Tank (Agitate2 hrs) Slurry Residue Coke C ake l Fimme Filfrme To furthur processing f(l6% of the weight (MOOJ'CU'Fe) (MOOJ'CU'Fe) of the Molybdenum in -NaOHstarting material as Final Product (Alzrecipitloitiorn lTsank d M us aan of the weight 1 p stand overnight) at the Molybdenum in startingmaterial Cake F iltrate Concentration of Cu on Metallic Fe SolutionFiltrate (Stand overnight) Cake Cake Filtrate 2% M0 0 To Discard Copperas a F incl Product INVENTOR.

STUART R. ZIMMERLEY EMlL E MALOUF ewx ATTORNEYS United States PatentACID PROCESS FOR PRODUCTION OF HIGH GRADE MOLYBDENUM OXIDE Stuart .R.Zimmerley and Emil E. Malouf, Salt Lake City, Utah, assignors toKennecott Copper Corporation, New York, N.Y., a corporation of New YorkFiled Oct. 10, 1957, Ser. No. 689,417

9 Claims. (Cl. 23-140) This invention relates to processes for theproduction of molybdenum oxide, and is concerned particularly withproviding a process applicable to low grade molybdenum sulfide flotationconcentrates.

Molybdenum oxide is presently produced commercially from molybdenumsulfide flotation concentrates by passing such concentrates throughconventional roasting apparatus, such as the well known Herreshoffmultiple hearth furnace, where the sulfides are oxidized by the actionof heat in the presence of air.

Much of the concentrates so processed are obtained as a by-product ofthe recovery, by flotation, of copper minerals from low grade coppersulfide ores.

All of such concentrates are not of the same quality, however. Some areinferior as compared with others, even when run through special andexpensive upgrading procedures. Accordingly, they bring a lower price onthe market and are diflicult to dispose of when plentiful supplies ofhigher grade concentrates are available. Their inferior quality is duelargely to copper and iron contamination. It is to molybdenum sulfideconcentrates of this type that our invention is especially, though by nomeans exclusively, applicable.

The present invention is closely related to one forming the subject ofour copending application Serial Num ber 771,161, filed October 31,1958, entitled Acid Process for Recovery of Rhenium from MineralMaterials Containing Same, now abandoned, which is acontinuation-in-part of our similarly entitled application Serial Number592,182, filed June 18, 1956, and now abandoned. When justified by thecharacter of the concentrates being treated, the present process will benormally carried out in conjunction with the recovery of rhenium bymeans of the process of our aforesaid copendin-g application.Nevertheless, the process of this present invention may beadvantageously utilized whether or not a recoverable quantity of rheniumis contained .in the molybdenum sulfide concentrate being treated.

By the process, the molybdenum is solubilized, so that the resultingproduct may be treated by chemical, ionexchange, or liquid-liquidextraction methods for the re covery of valuable by-products, such ascopper, rhenium, and selenium, as well as for the production of anextremely high purity molybdenum oxide. Other decided advantages overthe ordinary commercial roasting are that dust loss is reducedappreciably, and the usual loss of molybdenum oxide by volatilization(when roasting to the lowest possible sulfur content) is eliminated.

Impurities and valuable by-products often present in molybdeniteflotation concentrates are aluminum, antimony,'barium, beryllium,bismuth, calcium, chromium, cobalt, copper, germanium, indium, iron,lead, lithium, magnesium, manganese, nickel, phosphorus, rhenium,selenium, silicon, silver, sodium, sulfur, tin, titanium, vanadium,zinc, and zirconium.

By our process, impurities are removed in three ways. Some impurities,such as selenium, rhenium, phosphorus,

2,955,447 Patented Dec. 20, 1960 and sulfur. are eliminated byvolatilization during a preliminary roasting stage and also, thereafter,during an oxidizing acid roast which characterizes the process. Someimpurities, such as copper and iron, are converted to Water soluble formremovable from the final calcines by water leaching. Those impuritiesthat are not volatilized or solubilized form insoluble compounds whichsettle out as a sludge.

An example of the amount of purification that can be obtained by thisprocess is shown by the upgrading of a molybdenite concentrate from68.88 percent molybdenum sulfide to 98.7 percent molybdic oxide. By theconventional roasting method of producing molybdic oxide, the 68.88percent molybdenum sulfide concentrate would have produced only a 62percent molybdic oxide.

In accordance with the invention, and as a principal object thereof,molybdenum oxide of exceptionally high purity is obtained from eveninferior grades of molybdenum sulfide concentrates. In addition,contaminating copper is economcially recoverable.

The process of the invention is characterized by the subjection of themolybdenum sulfide concentrates to the combined action of heat and anoxidizing, strong, mineral acid following the oxidation of a large partor all of the sulfur by preliminary roasting.

Further objects and features of the invention will become apparent fromthe following detailed description of the preferred procedures indicatedby the flow sheet of the accompanying drawing, which represents aparticular preferred practice of the process.

Referring to the drawing:

in applying our process to any given molybdenum sulfide flotationconcentrate, such concentrate is preferably subjected to a preliminaryrorsting operation for the oxid"tion of a large part, if notsubstantially all, of its sulfur content.

In instances where the rhenium content of the concentrate issufficiently high to make recovery practical, for ex mple withconcentrates from the Nevada Consolidated Division and the Chino MinesDivision of Kennecott Copper Corporation, this preliminary roast iscarefully controlled to eliminate approximately 40 to 50% of the sulfurwithout volatilizing any significant quantity of the rhenium ormolybdenum. For this purpose, the roasting operation is generallyconducted in a multiple hearth, rabble type roaster at a temperature ofapproximately 600 degrees centigrade for approximately two hours, as ismore fully disclosed in our copending application Serial Number 771,161,previously referred to. The gaseous effluent from such operation isadvantageously passed through particle collecting apparatus and a gasscrubber for recovery of that rhenium which is volatilized.

In instances where the rhenium content of the concentrate is either tooinsignificant to be recovered, or for some reason is not of interest tothe producer of molybdenum oxide, the preliminary roasting operation ispreferably carried on until most or substantially all of the sulfur isoxidized, usually, over a period of approximately four hours at about600 degrees centigrade.

As mentioned hereinbefore, the present process is most advantageous inits application to molybdenum sulfide concentrates of inferior quality,but it may also be applied to advantage to relatively high gradeconcentrates where an exceptionally high purity product is desired.

In all instances, the calcine from the roaster is charged intopreferably a rotary furnace, for example, a standard Bruckner typefurnace, along with a quantity of a concentrated and preferablyoxidizing, strong, mineral acid. While any mineral acid may besuccessfully utilized under oxidizing conditions, it is preferred toemploy sulfuric acid because of its oxidizing character, itsavailability in quantity, and its comparatively low cost.

The quantity of acid utilized in any given instance will be sufficientto thoroughly wet the concentrate, and will depend largely upon theextent to which the preliminary roasting operation has been carried.Where only 40% to 50% of the sulfur has been eliminated from theconcentrate, as where rhenium is being recovered, the quantity ofsulfuric acid employed should be approximately two parts of acid to onepart of calcine by weight. Where approximately 80% or more of the sulfurhas been eliminated, the quantity of acid can be reduced to a ratio ofone part of acid to one part of the calcine. It should be borne in mind,however, that in the latter instance, a substantial portion of anyrhenium present is volatilized during the preliminary roast, i.e. from25% to 40%.

The mixture of calcined molybdenum sulfide concentrate and mineral acidis heated to a temperature within the range of from approximately 300degrees to 400 degrees centigrade for a period of about eight hours,during which time certain of the unvolatilized contaminants in theoriginal concentrate (notably copper and iron) are rendered solublealong with the molybdenum. The material from this acid-heating stage isan easily handled powder.

Where rhenium is to be recovered, the two stage acidheating of ouraforementioned copending application Serial Number 771,161 is applied inorder to first oxidize the rhenium, without volatilizing either it orthe acid, and1 subsequently to volatilize both the rhenium and the am Inall instances, the material from the rotary furnace is leached withwater (preferably an equal weight) in any suitable leach tank and for aperiod of approximately two hours under conditions of agitation, duringwhich time copper, iron, and any other solubilized contaminants aredissolved and leached out along with the molybdenum oxide.

The insolubles form a residue at the bottom of the tank, while theliquid and some molybdenum oxide which has already precipitated out ofsolution form a slurry in the upper portion of the tank.

The slurry is decanted from the leach tank and is passed to a filter ofany suitable type, for example, a multiple-leaf vacuum filter, where thesolids are formed into a filter cake containing a high percentage of themolybdenum present in the starting material. Such molybdenum is in theform of a high grade molybdenum oxide (approximately 82% by Weight of98.7% M is typical).

The liquid filtrate, carrying principally molybdenum oxide, copper, andiron in solution, and filtrate resulting from filtration of the residueof the leach tank left after decanting of the slurry, are combined, andthe pH thereof is adjusted to a less acid condition (e.g. to 1.5) by theaddition of a basic material that will not combine with the molybdateion (e.g. NaOH), to selectively precipitate molybdenum oxide. Thesolution containing the precipitated molybdenum oxide is then filtered.The resulting filter cake is combined with the previously recoveredfilter cake to provide a molybdenum oxide product of grade considerablyhigher than obtained by ordinary roasting procedures.

The filter cake resulting from filtration of the leach tank residuecontains some molybdenum (16% of the weight of the molybdenum in thestarting material as 85% M00 which may be recovered by furtherprocessing in known manner.

The final filtrate is treated for the recovery of copper, preferably bycementation on iron. Thereafter, further filtration of such finalfiltrate solution yields a filter cake high in copper and a filtrate,which, after standing, may be filtered further to yield a cakecontaining sufiicient M0 0 (approximately 2%) to have some commercialvalue.

Whereas this invention is here specifically set forth with respect topresently preferred procedure, it is to be understood that variouschanges may be made without departing from the scope of the claims whichhere follow.

We claim:

1. A process for producing high grade molybdenum oxide, comprisingroasting a molybdenum sulfide concentrate containing impurities,including at least copper and iron, at a temperature below that at whichmolybdenum oxide volatilizes to oxidize a large portion of its sulfurcontent in the form of a gaseous effiuent; thoroughly wetting thecalcine from such roasting operation with a concentrated, strong,mineral acid; heating the wetted calcine in the presence of oxygen at atemperature within the range of from approximately 300 degrees toapproximately 400 degrees centigrade for a sufiicient length of time tooxidize the molybdenum sulfide and solubilize at least the copper andiron present; leaching the resulting calcine with water under conditionsof agitation to produce an aqueous solution containing molybdenum oxideand water soluble impurities; separating the pregnant leach solutionfrom the insoluble residue; and recovering molybdenum oxide as a highgrade product free of said water soluble impurities by precipitatingsaid molybdenum oxide from said pregnant leach solution on standing, andfreeing the precipitate from the solution.

2. The process of claim 1, wherein the molybdenum sulfide concentrate isroasted for a period of approximately two hours at about 600 degreescentigrade, the gaseous effiuent therefrom being treated for therecovery of rhenium; and wherein the calcine from such roasting operation is wetted with approximately twice its weight of the mineralacid.

3. The process of claim 1, wherein the molybdenum sulfide concentrate isroasted for a period of approximately four hours at about 600 degreescentigrade; and wherein the calcine from such roasting operation iswetted with approximately an equal weight of the mineral acid.

4. A process for producing high grade molybdenum oxide, comprisingroasting a molybdenum sulfide concentrate containing impuritiesincluding at least copper and iron at a temperature below that at whichmolybdenum oxide volatilizes; to oxidize a large portion of its sulfurcontent in the form of a gaseous efiiuent; thoroughly wetting thecalcine from such roasting operation with a concentrated, strong,mineral acid; heating the wetted calcine in the presence of oxygen at atemperature within the range of from approximately 300 degrees toapproximately 400 degrees centigrade for a suflicient length of time tooxidize the molybdenum sulfide and solubilize at least the copper andiron present; leaching the resulting calcine with water under conditionsof agitation to produce an aqueous solution containing molybdenum oxideand water soluble impurities; separating the pregnant leach solutionfrom the insoluble residue; raising the pH of the pregnant leachsolution until molybdenum oxide precipitates therefrom, leaving saidwater soluble impurities behind in the solution; and separating theprecipitated molybdenum oxide from the solution.

5. The process of claim 4, wherein the molybdenum sulfide concentrate isroasted for a period of approximately two hours at about 600 degreescentigrade, the gaseous effluent therefrom being treated for therecovery of rhenium; and wherein the calcine from such roastingoperation is wetted with approximately twice its weight of the mineralacid.

6. The process of claim 4, wherein the molybdenum sulfide concentrate isroasted for a period of approximately four hours at about 600 degreescentigrade; and wherein the calcine from such roasting operation iswetted with approximately an equal weight of the mineral acid.

7. The process of claim 1, wherein the recovery of molybdenum oxidecomprises precipitating molybdenum oxide from the pregnant leachsolution on standing, leaving less easily precipitated molybdenum oxidein the t n g ther with the water soluble impurities; separating saidsolution from the precipitated molybdenum oxide; precipitatingadditional molybdenum oxide from the so-separated solution on standingby raising the pH of that solution to approximately 1.5; and freeingsaid additional molybdenum oxide from the solution.

8. The process of claim 1, wherein the mineral acid is sulfuric acid.

9. The process of claim 4, wherein the mineral acid is sulfuric acid.

References Cited in the file of this patent UNITED STATES PATENTS1,399,554 Hamilton Dec. 6, 1921 6 Morgan Jan. 31, 1933 Herold et al May30, 1933 Driggs May 30, 1933 Maier Mar. 28, 1950 Bertolus Dec. 18, 1951Zimmerley et a1 Oct. 8, 1957 OTHER REFERENCES Mellor: ComprehensiveTreatise on Inorganic and 10 Theoretical Chemistry, Longmans, Green andCo., New

York, 1923, vol. II, pages 494, 496, 642.

UNITED STATES PATENT OFFICE CERTIFICATION OF CORRECTION Patent Nov2,965,447 December 20, 1960 Stuart R. Zimmerley et a1.

It is Hereby certified that error appears in the above numbered patentrequiring correction and that the said Letters Patent should read'ascorrected below.

Column 1, line 42, strike out "now abandoned,

Signed and sealed this 16th day of May 1961.

(SEAL) Attest:

ERNEST W. SWIDER DAVID L. LADD Attesting Officer Commissioner of Patents

1. A PROCESS FOR PRODUCING HIGH GRADE MOLYBDENUM OXIDE, COMPRISINGROASTING A MOLYBDENUM SULFIDE CONCENTRATE CONTAINING IMPURITIES,INCLUDING AT LEAST COPPER AND IRON, AT A TEMPERATURE BELOW THAT AT WHICHMOLYBDENUM OXIDE VOLATILIZES TO OXIDIZE A LARGE PORTION OF ITS SULFURCONTENT IN THE FORM OF A GASEOUS EFFLUENT, THROUGHLY WETTING THE CALCINEFROM SUCH ROASTING OPERATION WITH A CONCENTRATED, STRONG, MINERAL ACID,HEATING THE WETTED CALCINE IN THE PRESENCE OF OXYGEN AT A TEMPERATUREWITHIN THE RANGE OF FROM APPROXIMATELY 300 DEGREES TO APPROXIMATELY 400DEGREE CENTIGRADE FOR A SUFFICIENT LENGTH OF TIME TO OXIDIZE THEMOLYBDENUM SULFIDE AND SOLUBILIZE AT LEAST THE COPPER AND IRON PRESENT,LEACHING THE RESULTING CALCINE WITH WATER UNDER CONDITIONS OF AGITATIONTO PRODUCE AN AQUEOUS SOLUTION CONTAINING MOLYBDENUM OXIDE AND WATERSOLUBLE IMPURITIES, SEPARATING THE PREGNANT LEACH SOLUTION FROM THEINSOLUBLE RESIDUE, AND RECOVERING MOLYBDENUM OXIDE AS A HIGH GRADEPRODUCT FREE OF SAID WATER SOLUBLE IMPURITIES BY PRECIPITATING SAIDMOLYBDENUM OXIDE FROM SAID PREGNANT LEACH SOLUTION ON STANDING, ANDFREEING THE PRECIPITATE FROM THE SOLUTION.